1. Field of the Invention
This invention is related to a packet communication system with QoS control function, especially applicable to Diffserv.
2. Description of Related Art
Increase of Internet users, follows a sharp increase in the traffic (packets) that flows in the Internet. According to the packet communication mode used in the Internet, one line can carry packets from many users. Therefore, the packet communication mode reduces cost per a bandwidth. And strict management such as QoS (quality of service) control of every user, is not carried out in the Internet. This is also a factor of low cost of the Internet.
Telephone networks and company networks were constructed using exclusive lines respectively. But the low cost of the Internet has caused the movement of integrating telephone networks and company networks into the Internet for reduction of communication cost. For the integration, it is preferable to provide QoS guarantees such as low transmission delay, low packet discard rate, and so on, because those were realized in conventional telephone networks and company networks.
To provide the QoS guarantees, a packet is transmitted based on the priority of the packet that is decided by the agreement between a service provider (SP) and the network user, such as a company, with differentiating the applications, such as telephone traffic, or its respective users.
Japanese Unexamined Patent Publication Disclosure 6(1994)-197128 (related art (1)) shows a packet switching system that an output buffer for CBR and an output buffer for VBR are installed in every each output circuit. The output priority of a packet accumulated to the buffer for CBR is higher than that of a packet accumulated to the buffer for VBR.
Generally, an ATM (Asynchronous Transfer Mode) switching system sets a connection in advance according to an connection information table thereof. The connection information table also stores priority information.
But a router does not have a connection information table because a router, which is used in packet communication mode, does not set up a connection in advance. Therefore, to provide QoS guarantees by a router, it is required a flow detecting means that detects priority information of a packet based on information in the packet header. A router does priority transfer of a packet based on the priority information detected by the flow detecting means. In this specification, a condition for packet discrimination generated by information in the packet header, is called a flow condition. A series of traffic that meets the flow condition is called a flow. And processing that decides whether an input packet meets the flow condition, and decides necessary information for QoS control, such as priority information, is called flow detecting.
Japanese patent Laid-open print No. 6-232904 (related art 2) shows a priority control system in a router that decides relay processing priority from priority information and protocol information of a received packet.
On the other hand, Diffserv (differentiated services) is stated in RFC 2475 of IETF (Internet engineering task force) (related art 3). Using FIG. 2, we explain related art 3. Company networks 221, 222, 223, and 224 are mutually connected by the DS domain 225. The DS domain 225 executes the QoS control based on a policy such as TELNET is preferentially processed. As a result, QoS that contracts in advance between the enterprise network users and an administrator of DS domain 225, is provided. The DS domain 225 is composed of boundary node 226 and boundary node 227 that are positioned in the edge of the DS domain 225 and interior node 228 that is positioned in the core of the DS domain 225. Interior node 228 has much flow. And high-speed lines are connected to interior node 228. Therefore, interior node 228 may not be able to perform QoS control with high speed. Diffserv is a solution to that problem. The Interior node has only limited function because the load of the interior node is higher than that of the boundary node.
Suppose that a packet is transmitted from company network 221 to company network 224. When boundary node 226 receives a packet from company network 221, flow detection means (It is called Classifier in RFC 2475) of boundary node 226 performs flow detecting using the source/destination IP address, the source/destination port number, and the protocol in the TCP/IP header as flow condition. And it decides priority of the packet in the DS domain 225 and writes the priority into the DS field of the packet header. Boundary node 227 and interior node 228 with high load, performs flow detecting and QoS control with high speed based on only DS field value.